I think my boyfriends attracted to his niece...

I may be getting the wrong signals. But my boyfriends niece she's very pretty. Pretty face and nice body. Well my boyfriends baby mama looks similar to her. He always talks about his nieces ass which is huge! And he loves ass. Then will make sexual jokes with his niece. His niece will go out of her way to touch him but like caress his arm or hit him playfully. It's weird and then on Facebook he won't write to me or anyone else but he will go out of his way to leave comments on her posts. Idk maybe I'm exaggerating it all. It's just a weird "family relationship" with them. I've just never seen or had with them men in my family. Anyone else?